Methods of toughening a glass sheet

ABSTRACT

A glass sheet is toughened by quenching the sheet after it has been contacted by shaping surfaces. Prior to quenching, for example in a chilling liquid, the glass sheet is heated throughout is bulk to a pre-quenching temperature which is higher than the temperature of the glass while it was being shaped.

Ill/ll O Umted States Patent 1191 1111 3,914,1 19 Jack et al. [4 Oct.21, 1975 [54] METHODS OF TOUGHENING A CLASS 3,341,313 9/1967 Wheeler etal. 65/104 SH ET 3,365,285 1/1968 Richardson 65/104 3,701,266 10/1972Chisholm 65/104 X [75] Inventors: Harry Ross Scarlett Jack,

Tanw r h-in-A Arthur Jo eph FOREIGN PATENTS 0R APPLICATIONS NobbsAlvechurch of England 1.241.524 8/1971 United Kingdom 65/104 [73]Assignee: Triplex Safety Glass Company Lmmed London England PrimaryExaminer-Arthur D. Kellogg [22] Filed: Mar. 12, 1974 Attorney, Agent, orFirm-Burns, Doane, Swecker &

' h. 211 Appl. No.: 450,371

[30] Foreign Application Priority Data [57] ABSTRACT July 20, 1973United Kingdom 34705/73 A glass Sheet is toughened y quenching the sheetafter it has been contacted by shaping surfaces. Prior 65/104 ig g g toquenching, for example in a chilling liquid, the glass [58] i H4 116sheet is heated throughout is bulk to a pre-quenching 0 temperaturewhich is higher than the temperature of [56] References Cited the glasswhile it was being shaped.

UNITED STATES PATENTS 25 Claims, 25 Drawing Figures 2,442,242 5/1948Lewis 65/104 X US. Patent Oct. 21, 1975 Sheet10f23 3,914,119

US. Patent Oct. 21, 1975 Sheet2of23 3,914,119

US. Patent Oct. 21, 1975 Sheet 3 of 23 3,914,119

U.S. Patent Oct. 21, 1975 Sheet4of23 3,914,119

U.S. Patent Oct. 21, 1975 Sheet5of23 3,914,119

U.S. Patent Oct. 21, 1975 Sheet7of23 3,914,119

W/M/V BOO AY MAWAW US. Patent 0.21,1975 Sheet9 0f23 3,914,119 1 He. /OB.

U.S. Patent Oct.21, 1975 Sheet 10 0f23 3,914,119

U.S. Patent Oct. 21, 1975 Sheet110f23 3,914,119

US. Patent Oct. 21, 1975 Sheet 12 of 23 3,914,119

U.S. Patent Oct. 21, 1975 Sheet 13 of 23 3,914,119

C. E m a 6 US. Patent Oct.21, 1975 Sheet 14 0f23 3,914,119

Ha. HA.-

US. Patent 0.21, 1975 Sheet 15 of 23 3,914,119

He. BB

US. Patent Oct. 21, 1975 'Sheet 16 of 23 3,914,119

US. Patent Oct. 21, 1975 Sheet l7 of 23 3,914,119

US. Patent Oct. 21, 1975 Sheet 18 0f23 3,914,119

Sheet 19 of 23 U.S. Patent Oct. 21, 1975

1. IN A METHOD OF TOUGHENING A GLASS SHEET WHEREIN THE GLASS SHEET ISHEATED TO A PREDETERMINED TEMPERATURE CONDITION IN WHICH CONDITION ITCAN BE BENT, GLASS-BENDING DIES ARE CLOSED ON TO THE SHEET, THOSEBENDING DIES ARE RETRACTED FROM THE SHEET, AND THE SHEET IS TOUGHENED BYCONTACTING ITS SURFACES WITH A CHILLING MEDIUM, THE IMPROVEMENTCOMPRISING: AFTER BENDING AND PRIOR TO TOUGHENING OF THE BENT SHEET,CONTROLLABLE PASSNG THE BENT GLASS SHEET THROUGH A HEATING ZONE TOESTABLISH SUFFICIENT RESIDENCE OF SAID SHEET IN THE HEATING ZONE SO ASTO HEAT THE SHEET SUBSTANTIALLY UNIFORMYL THROUGHOUT ITS THICKNESS TO APRE-QUENCHING TEMPERATURE CONDITION ABOVE THE TEMPERATURE AT WHICH ITLEAVES THE GLASS BENDING DIES BUT AT WHICH THE SHEET REMAINS BENT FORQUENCHING THE BENT SHEET.
 2. A method according to claim 1, wherein thestep of contacting the surfaces of the bent sheet with a chilling mediumincludes the preliminary step of subjecting the glass sheet to coolinggas streams to induce surface-to-centre temperature gradients throughThe thickness of the glass sheet.
 3. A method according to claim 1wherein the glass is heated to a predetermined bending temperature, andthe bending dies are maintained at the same temperature as said bendingtemperature.
 4. A method according to claim 3, wherein the glass is asheet of soda-lime-silica glass, said bending temperature is in therange 570* to 650*C and said pre-quenching temperature is in the range620* to 720*C.
 5. A method according to claim 1, wherein the bent glasssheet is heated to said pre-quenching temperature condition to increasethe temperature substantially uniformly throughout the thickness of thesheet and to induce a substantially linear temperature gradient in theglass sheet from a higher temperature in the region of the leading edgeof the sheet which contacts the chilling medium first to a lowertemperature in the region of the trailing edge of the sheet.
 6. A methodaccording to claim 5, wherein the heating of the bent glass sheetcomprises lowering the bent glass sheet at a first speed through saidheating zone which is of greater depth than the height of the sheet intoa zone where it contacts the chilling medium, and at a predeterminedtime after entry of the lower edge of the sheet into the heating zonewhile the upper edge of the sheet is still within the heating zone,accelerating the sheet to a second higher speed for entry into thechilling medium, thereby heating the lower edge of the sheet to a highertemperature than the upper edge.
 7. A method according to claim 6,wherein the sheet is accelerated to said second higher speed when thelower edge of the sheet reaches the bottom of the heating zone.
 8. Amethod according to claim 5, wherein the glass sheet is a sheet ofsoda-lime-silica glass which prior to bending is within the temperaturerange 570* to 650*C. and which when heated to said pre-quenchingtemperature condition is within the temperature range 620* to 720*C. 9.A method according to claim 8, wherein the leading edge of the glasssheet is from 5* to 30*C hotter than the trailing edge of the sheet. 10.A method according to claim 9, wherein the leading edge of the sheet is20*C hotter than the trailing edge of the sheet.
 11. A method accordingto claim 10, wherein said substantially linear temperature gradient isinduced in the glass sheet from 700*C. at the leading edge of the sheetto 680*C. at the trailing edge of the sheet.
 12. In a method oftoughening a glass sheet wherein the glass sheet is heated to apredetermined temperature condition in which condition it can be shaped,glass-shaping surfaces are closed on to the sheet, those surfaces areretracted from the sheet, and the shaped sheet is toughened bycontacting its surfaces with a chilling medium, the improvementcomprising: after shaping and prior to toughening of the shaped sheet,controllably passing the shaped glass sheet through a heating zone toestablish sufficient residence of said sheet in the heating zone so asto heat the sheet substantially uniformly throughout its thickness to apre-quenching temperature condition above the temperature at which itleaves the glass shaping surfaces but at which the sheet remains shapedfor quenching of the shaped sheet.
 13. A method according to claim 12wherein the step of contacting the surfaces of the shaped sheet with achilling medium includes the preliminary step of subjecting the glasssheet to cooling gas streams to induce surface-to-centre temperaturegradients through the thickness of the glass sheet.
 14. A methodaccording to claim 12 wherein the glass sheet is heated to apredetermined shaping temperature, and the glass shaping surfaces aremaintained at the same temperature as said shaping temperature.
 15. Amethod according to claim 14 wherein the glass is a sheet ofsoda-lime-silica-glass, said shapinG temperature is in the range 570* to650*C. and said pre-quenching temperature is in the range 620* to 720*C.16. A method according to claim 12 wherein the shaped glass sheet isheated to said pre-quenching temperature condition to increase thetemperature substantially uniformly throughout the thickness of thesheet and to induce a substantially linear temperature gradient in theglass sheet from a higher temperature in the region of the leading edgeof the sheet which contacts the chilling medium first to a lowertemperature in the region of the trailing edge of the sheet.
 17. Amethod according to claim 16 wherein the heating of the shaped glasssheet comprises lowering the shaped glass sheet at a first speed throughsaid heating zone which is greater depth than the height of the sheetinto a zone where it contacts the chilling medium, and at apredetermined time after entry of the lower edge of the sheet into theheating zone while the upper edge of the sheet is still within theheating zone, accelerating the sheet to a second higher speed for entryinto the chilling medium, thereby heating the lower edge of the sheet toa higher temperature than the upper edge.
 18. A method according toclaim 17 wherein the sheet is accelerated to said second higher speedwhen the lower edge of the sheet reaches the bottom of the heating zone.19. A method according to claim 16 wherein the glass sheet is a sheet ofsoda-lime-silica glass which prior to shaping is within the temperaturerange 570* to 650*C. and which when heated to said pre-quenchingtemperature condition is within the temperature range 620* to 720*C. 20.A method according to claim 19 wherein the leading edge of the sheet is20*C. hotter than the trailing edge of the sheet.
 21. A method accordingto claim 20 wherein said substantially linear temperature gradient isinduced in the glass sheet from 700*C. at the leading edge of the sheetto 680*C. at the trailing edge of the sheet.
 22. In a method oftoughening a glass sheet wherein the glass sheet is heated to apredetermined temperature condition in which condition it can be shaped,glass-shaping surfaces are closed on to the sheet, those surfaces areretracted from the sheet, and the shaped sheet is toughened bycontacting its surfaces with a chilling medium, the improvementcomprising: after shaping and prior to toughening of the shaped sheet,passing the shaped glass sheet between heaters which are at atemperature in the range 750* to 1600*C., in a transit time of between1.3 and 45 seconds, which transit time is sufficient to heat the sheetsubstantially uniformly throughout its thickness to a pre-quenchingtemperature condition at least 10*C. above the temperature at which itleaves the glass shaping surfaces but at which the sheet remains shapedfor quenching of the shaped sheet.
 23. The method of claim 13 whereinthe sheet is heated to said pre-quenching temperature condition at least60*C. above the temperature at which it leaves the glass shapingsurfaces.
 24. In a method of toughening a glass sheet wherein the glasssheet is heated to a predetermined temperature condition in whichcondition it can be shaped, glass-shaping surfaces are closed on to thesheet, those surfaces are retracted from the sheet, and the shaped sheetis toughened by contacting its surfaces with a chilling medium, theimprovement comprising: after shaping and prior to toughening of theshaped sheet, passing the shaped glass sheet between heaters which areat a temperature in the range 750* to 1600*C, in a transit time ofbetween 1.3 and 45 seconds, which transit time is sufficient to heat thesheet substantially uniformly throughout its thickness to apre-quenching temperature from 10* to 140*C. above the temperature Atwhich it leaves the glass shaping surfaces but at which the sheetremains shaped for quenching of the shaped sheet.
 25. In a method oftoughening a glass sheet wherein the glass sheet is heated to apredetermined temperature condition in which condition it can be bent,glass-bending dies are closed on to the sheet, those bending dies areretracted from the sheet, and the sheet is toughened by contacting itssurfaces with a chilling medium, the improvement comprising: afterbending and prior to toughening of the bent sheet, passing the bentglass sheet between heaters which are at a temperature in the range 750*to 1600*C., in a transit time of between 1.3 and 45 seconds, whichtransit time is sufficient to heat the sheet substantially uniformlythroughout its thickness to a pre-quenching temperature from 10* to140*C. above the temperature at which it leaves the glass bending diesbut at which the sheet remains bent for quenching the bent sheet.